The present invention relates to a transmitting-receiving apparatus and, more specifically to a wireless transmitting-receiving apparatus suitable for use in a speedometer of a bicycle and the like.
Currently, a speedometer is often attached to two-wheeled vehicles and, especially on bicycles so as to show, in a simple manner, the speed of travel, the distance of travel and the like information. In a known speedometer, a rotation sensor is attached to a fork, the body of the speedometer is attached to the handlebar by means of a bracket, and the sensor and the bracket are connected to each other by a cord, as shown, for example, in Japanese Patent Laying Open No. 57-149967. Signals generated based on the rotation of the front wheel of the bicycle are inputted to the speedometer through the cord, and the speed of travel of the bicycle is calculated and displayed based on the signals.
The cord of a speedometer as described above can be broken or damaged by the vibration during travel, as the cord is arranged along the fork. In addition, the appearance of such cord is not very desirable. In order to eliminate such disadvantages of the speedometer having such cords, wireless transmission of the rotational signal instead of the use of cords has been proposed. However, it is impossible to use a wide space to mount a power supply on a bicycle. Therefore, in order to employ a wireless speedometer for a bicycle, the signals must be transmitted by a transmission unit of low power consumption and the signals must be received by a highly sensitive receiving unit of low power consumption. In such structure, the receiving unit becomes sensitive to external noises, as the output of the transmitted signal is low. In addition, erroneous signals are likely to be generated due to mechanical or physical vibration and shock during traveling. For example, the speedometer is adapted to calculate the speed of travel of a bicycle, such that the rotary signal is outputted as one pulse signal per one rotation of the wheel of the bicycle, the number of generation of the pulse signals are counted, and the speed of travel of the bicycle is calculated based on the counted value. When vibration or shock generating signals similar to the pulse signals are applied to the receiving unit or the transmitting unit, the pseudo signals may be counted as proper pulse signals. As a result, the speed of the bicycle cannot be accurately counted or displayed.
The foregoing is a problem not only of the speedometer for bicycles, but it is common to all wireless transmitting/receiving apparatuses used under similar conditions.